Determination of the absolute configuration of a novel dipeptide isostere

(1R-[1 alpha(1R*,2R*,3S*),2 beta,5 alpha])-2-(4-Morpholinocarbonyl)- 3-phenylcyclopropane 2-(1-methyl-ethyl)-5-methylcyclohexyl ester, C25H35NO4, Mr = 413 x 56, orthorhombic, P2(1)2(1)2(1), a = 9 x 359 (2), b = 10 x 1172 (14), c = 24 x 710 (4) A, V = 2339 x 8 (6) A3, Z = 4, Dx = 1 x 17 g cm-3, mu = 0 x 7332 cm-1, Mo K alpha radiation, lambda = 0 x 7107 A, F(000) = 896, T = 198 K, R = 0 x 0475 for 2460 reflections [Fo greater than or equal to 4 sigma(Fo)]. The assignment of the absolute configuration was based on internal comparison to the (-)-menthol moiety. The morpholenyl and cyclohexyl rings are in the chair conformation. The amide group is essentially planar [max. deviation 0.025 (2) A for N19] resulting in a close non-bonded contact between the amide oxygen, O18, and H24a of 2 x 24 (4) A.